Method and apparatus for locking expandable cutters of well bore casing mill

ABSTRACT

A casing mill for downhole casing milling has multiple elongated cutter bases hingedly connected to a main body by a plurality of positioning arms. An operating mechanism within the main body of the casing mill, actuated by fluid flow, moves the cutter bases to an extended position. Multiple cutters fixed to the cutter bases are then positioned to engage a casing surface. An internal fluid operated locking mechanism can be selectively actuated to secure the cutter bases in an extended position.

FIELD OF THE INVENTION

The present invention pertains to a mill or cutting assembly for the downhole cutting of tubular goods in wellbores. More particularly, the present invention pertains to a downhole mill or cutting assembly having radially or outwardly extending cutter bases. More particularly still, the present invention pertains to a locking assembly for securing cutting bases of a downhole mill or cutting assembly in a radially or outwardly extended position during use.

DESCRIPTION OF RELATED ART

It is often desirable, and sometimes necessary, to conduct downhole operations within a wellbore for any number of different reasons. One common downhole operation involves the plugging and abandonment of depleted wells.

After hydrocarbon reserves accessible from a well have been fully recovered, the wellbore must eventually be plugged and abandoned and the well site restored to its original condition.

Typically, as much production tubing and casing as possible is retrieved from a well as part of the plugging and abandonment process. In many cases, such recovered tubular goods can be reused in other wells or sold for salvage. However, because the pipe—and especially the casing—can be cemented or otherwise secured in place within a wellbore, downhole blades or other cutting devices are frequently required to cut the pipe at desired depths in the well prior to removal. In many cases, such cutting equipment is conveyed in and out of a well via tubular workstring. After desired down-hole cut(s) are made, the workstring and the severed pipe are typically pulled out of the well from the surface.

Various tools have been developed for downhole cutting or severing of casing strings in wellbores, and for cutting or milling window sections in casing strings. Generally, such tools have comprised a main body with multiple hinged arms or blades, which are rotated outwardly into contact with the casing (by hydraulic or other means) when the tool is in position downhole. Fluid is typically pumped down through the tubular drillstring and the tool in order to actuate the mechanism and rotate the blades outward. Once the blades are rotated outwardly toward the surrounding casing, rotation of the drillstring (and tool) causes the cutting surfaces on the blades to cut through the casing string. Fluids are pumped through the system to lift cuttings or shaving debris to the surface.

Conventional cutting tools cannot efficiently cut or sever multiple, cemented-together casing strings and, in particular, cannot efficiently cut “windows” in such strings; as used herein, the term “window” means the cutting or milling of a section (e.g., 20′ or more) of the casing string, as opposed to simply severing the casing string. In addition, conventional downhole tools tend to create long, connected metal shavings which must be lifted (or “circulated”) from a wellbore by fluid flow, or else said shavings can become nested together downhole and potentially cause the drillstring to become stuck within a wellbore.

In an effort to overcome such limitations, a downhole cutting assembly has been developed having a plurality of elongated cutter bases hingedly connected to a main body. Said elongated cutter bases are connected to said main body using a plurality of linkage arms, and are movable from a first position substantially recessed into said main body, to a second position extended radially outwardly from the main body. An operating mechanism within the main body, operable by fluid flow, moves the linkage arms and cutter bases between said positions. The linkage arms hold the cutter bases substantially parallel to the axis of the main body; a plurality of cutter blades or “knives” is mounted on the cutter bases, and engages the casing string when the cutter bases are in said (second) outwardly extended position.

Although such cutting devices are effective, problems can arise when the annular gap—that is, the distance between the outside of the body member and the inner surface of the casing to be milled—is relatively small. For example, when the angle of attack of a linkage arm with the casing is less than about 20 degrees, or when the casing is equipped with flush joint connections which prevent such linkage arms from fully extending or expanding radially outward from said body member, said linkage arms can tend to collapse inward after some period of use. Frequently, tapered cutting blades or knives, together with the weight of the assembly and/or an attached workstring, can result in unwanted collapsing of said linkage arms.

Thus, there is a need for means to lock said linkage arms of a downhole cutting assembly in a radially outward or extended position, particularly when tapered cutting blades are utilized, and/or when the annular gap or distance existing between the outside of the body member and the inner surface of the casing to be milled is relatively small.

SUMMARY OF THE INVENTION

In a preferred embodiment, the present invention comprises a well bore casing mill or cutting assembly having expandable cutter bases. Said casing mill, embodying the principles of the present invention, comprises a main body having a longitudinal bore therethrough. Means for connecting the main body to a drill string, typically threaded connections, are provided on at least the upper end of said main body.

A plurality of elongated cutter bases are hingedly connected to said main body by a plurality of linkage arms, and are movable from a first position substantially recessed into the main body, to a second position extended outwardly from the main body. An operating mechanism within the main body, operable by fluid flow, moves the linkage arms and cutter bases. The linkage arms hold the cutter bases substantially parallel to the axis of the main body. A plurality of cutters is mounted on the cutter bases, and engages the casing string when the cutter bases are in an outwardly extended (cutting) position.

A piston assembly comprises a piston body having a plurality (typically three) pockets or recesses, each for receiving a lock button. Each lock button is retained in place within a pocket or recess using a spring and spring retainer. Nozzle(s) are beneficially positioned in proximity (typically below) said lock button pockets or recesses. Said piston body is slideably received within a lock ring held said body using at least one shear screw. A piston stop is provided to prevent backward movement of said piston, particularly while tripping in hole with the cutting assembly of the present invention.

In operation, the cutting assembly of the present invention can be tripped or run in a wellbore to a desired depth. After reaching said depth, said cutting assembly can be selectively activated by pumping fluid through said nozzle at a predetermined flow rate. When a predetermined fluid pressure acting on the piston (which, by way of illustration but not limitation, can typically be in a range between 1000-2200 psi) is achieved, force will act on a drive link cam opening the cutter arms to which the knives are attached.

Said piston further comprises at least one lock button. When said fluid is pumped through said nozzle(s), said at least one lock button will be exposed to the same fluid pressure. Force resulting from said fluid pressure will cause said at least one lock button to move radially outward until it engages against a lock ring sleeve. In a preferred embodiment, said lock ring sleeve has threads or ridges that are designed to hold loading in only one axial direction. As such, said at least one lock button and lock ring cooperate to act as ratchet assembly; said ratchet assembly will provide resistance to prevent said arms from collapsing, while allowing substantially free movement in opposite axial direction. The loads acting on lock ring sleeve are equally distributed between the lock button(s).

During operation within a wellbore, the present invention will ensure that cutter arm do not collapse inward when said cutting assembly is used, even in casings having a relatively small inner diameter or casings with flush connections. Further, when the pumping of fluid ceases, a differential pressure will also cease, thereby allowing said spring(s) to bias said lock button(s) away from the lock ring sleeve. In this manner, said linkage arms can be easily collapsed inward, such as when the cutting assembly is being retrieved or pulled out of a wellbore.

In the event that said piston does not collapse as desired when pumping of fluid ceases, the cutting assembly can be picked up using a tubular workstring. In such a scenario, the axial force applied to said cooperating lock button(s) and lock sleeve is increased until said shear screw(s) holding said lock ring sleeve in place will shear at a predetermined or preset force. After the shear screw(s) shear, said lock ring sleeve can move, thereby disengaging from said lock button(s) and permitting said linkage arms to collapse radially inward toward said body member.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as any detailed description of the preferred embodiments, is better understood when read in conjunction with the drawings and figures contained herein. For the purpose of illustrating the invention, the drawings and figures show certain preferred embodiments. It is understood, however, that the invention is not limited to the specific methods and devices disclosed in such drawings or figures.

FIG. 1 depicts a side view of a wellbore cutting assembly of the present invention in a retracted configuration.

FIG. 2 depicts an alternate side view of a wellbore cutting assembly of the present invention in a retracted configuration (rotated approximately 90-degrees about its longitudinal axis from the view depicted in FIG. 1).

FIG. 3 depicts a side view of a wellbore cutting assembly of the present invention in an extended configuration.

FIG. 4 depicts an alternate side view of a wellbore cutting assembly of the present invention in an extended configuration (rotated approximately 90-degrees about its longitudinal axis from the view depicted in FIG. 3).

FIG. 5 depicts a perspective exploded view of a wellbore cutting assembly of the present invention.

FIGS. 6A and 6B depict a side sectional view of a wellbore cutting assembly of the present invention along line 6-6 of FIG. 2.

FIGS. 7A and 7B depict a side sectional view of a wellbore cutting assembly of the present invention along line 7-7 of FIG. 4.

FIG. 8 depicts a detailed view of the highlighted portion of FIG. 6B.

FIG. 9 depicts a detailed view of the highlighted portion of FIG. 7B.

FIG. 10 depicts a perspective exploded view of a locking assembly of the present invention.

FIG. 11 depicts a sectional view of a wellbore cutting assembly of the present invention along line 11-11 of FIG. 2.

FIG. 12 depicts a sectional view of a wellbore cutting assembly of the present invention along line 12-12 of FIG. 2.

FIG. 13 depicts a detailed side view of the highlighted portion of FIG. 8.

FIG. 14 depicts a detailed side view of the highlighted portion of FIG. 9.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

This application incorporates the following disclosures in their entirety as if fully set forth herein: U.S. Non-Provisional patent application Ser. No. 15/637,435 filed Jun. 29, 2017; U.S. Non-Provisional patent application Ser. No. 14/420,612 filed Feb. 9, 2015 (subsequently issued as U.S. Pat. No. 9,695,660); PCT Application Serial No. PCT/US2013/053770, filed Aug. 6, 2013; and U.S. Provisional Patent Application Ser. No. 61/681,670, filed Aug. 10, 2012.

While the present invention will be described with reference to preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the present invention not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments (and legal equivalents thereof).

Referring to the drawings, FIG. 1 depicts a side view of a wellbore cutting assembly 10 of the present invention in a retracted configuration, while FIG. 2 depicts an alternate side view of said wellbore cutting assembly 10 in said retracted configuration. The views of wellbore cutting assembly 10 depicted in FIGS. 1 and 2 are rotated approximately 90-degrees about the longitudinal axis of said wellbore cutting assembly 10 relative to each other.

In a preferred embodiment, said wellbore cutting assembly 10 comprises a ported sub 60 connected to a body member 20. Although not depicted in FIGS. 1 and 2, said ported sub 60 has a means for connection and operational attachment to a tubular string, referred to herein as a drillstring or workstring, for conveying said cutting assembly 10 in and out of a wellbore, and manipulating said cutting assembly 10 in said wellbore, in a manner well known to those having skill in the art. Although other means for connection can be utilized, in a preferred embodiment said connection means comprises a threaded pipe connection. Although not shown in the embodiments depicted in FIGS. 1 and 2, if desired, it is to be observed that cutting assembly 10 can be configured with a lower threaded connection so that said cutting assembly 10 can be installed as a component within said drillstring or workstring.

Body member 20 has at least one elongate recess 28 defined or formed in exterior surfaces of said body member 20. At least one cutter base 30 is operationally attached to body member 20 using pivotally attached upper linkage or positioning arms 50, and pivotally attached lower linkage or positioning arms 51. In the collapsed configuration depicted in FIGS. 1 and 2, each of said at least one cutter bases 30 is in a radially or inwardly collapsed position, and is received within an elongate recess 28. In a preferred embodiment, a plurality of blades or cutters is mounted on an exterior portion of said cutter bases 30 (for space and clarity, not all of cutters 40 are labeled or annotated in the attached drawings). In the embodiment depicted in the drawings, wellbore cutting assembly 10 has two cutter bases 30; however, it is to be observed that other numbers or configurations of cutter bases 30 can be attached to body member 20 within the scope of the present invention.

FIG. 3 depicts a side view of a wellbore cutting assembly 10 of the present invention in an extended configuration, while FIG. 4 depicts an alternate side view of said wellbore cutting assembly 10 in said extended configuration. The view of wellbore cutting assembly 10 depicted in FIG. 4 is rotated approximately 90-degrees about the longitudinal axis of said cutting assembly 10 compared to the view depicted in FIG. 3.

Wellbore cutting assembly 10 comprises ported sub 60 having a means for connection and operational attachment to a tubular workstring (not visible in FIGS. 3 and 4). Ported sub 60 is attached to body member 20; said body member 20 has at least one elongate recess 28 defined or formed in the exterior of said body member 20. At least one cutter base 30 is operationally attached to body member 20, while a plurality of cutters 40 is mounted on an exterior portion of said cutter bases 30. Upper linkage or positioning arms 50 are pivotally attached to body member 20 using upper pivot pins 52, and to cutter base 30 using pivot pins 53. Similarly, lower linkage or positioning arms 51 are pivotally attached to body member 20 using lower pivot pins 54, and to cutter base 30 using pivot pins 55.

In a preferred embodiment, upper linkage arms 50 and lower linkage arms 51 are of substantially equal length. As such, it is understood that when cutter bases are in an extended position (as depicted in FIGS. 3 and 4), said cutter bases 30 are oriented substantially parallel to the longitudinal axis of body member 20. It is to be understood that cutter assembly 10 of the present invention encompasses different numbers of positioning arms 50 and 51; generally, a minimum of two are required (one actuated arm and at least one additional arm), but a greater number may be used depending upon the particular tool dimensions.

Wellbore cutting assembly 10 further comprises a means for moving cutter bases 30 from a first, retracted position (generally within body member 20 and not protruding significantly therefrom, as shown in FIGS. 1 and 2); to a second, extended position (wherein cutter bases 30 are partially or fully extended from body member 20, as depicted in FIGS. 3 and 4). Said means for moving cutter bases may comprise an operating mechanism generally utilizing fluid pumped down the bore of a drillstring and body member 20 to actuate said operating mechanism as more fully described herein.

FIG. 5 depicts a perspective exploded view of a wellbore cutting assembly 10 of the present invention. Referring to FIG. 5, wellbore cutting assembly 10 comprises ported sub 60 having a means for connection and operational attachment to a tubular workstring 200. Said ported sub 60 has lower threaded connection 61 for attachment to body member 20; in the embodiment depicted in FIG. 5, said lower threaded connection 61 comprises a male pin-end connection member having external threads well known to those having skill in the art.

Body member 20 has at least one elongate recess 28 defined or formed in the exterior of said body member 20. Although not visible in FIG. 5, it is to be observed that a structurally similar recess 28 is positioned on the opposite side of body member 20. At least one cutter base 30 is operationally attached to body member 20; said at least one cutter base 30 is beneficially positioned in alignment with said at least one recess 28. A plurality of upper linkage arms 50 having bores 50A and 50B are pivotally attached at one end to body member 20 using upper pivot pins 52. Said upper linkage arms 50 are also pivotally attached to said cutter bases 30 using pivot pins 53 via upper linkage clevis bracket member 34 having aligned bores 34A.

Still referring to FIG. 5, a plurality of lower linkage arms 51 having bores 51A and 51B are pivotally attached to clevis brackets 21 of body member 20 using lower pivot pins 54. Said lower linkage arms 51 are also pivotally attached to cutter bases using pivot pins 55. It is to be observed that said lower linkage arms 51 are received within lower linkage recesses 36 when said cutter bases 30 are in a radially collapsed configuration (for example, as depicted in FIGS. 1 and 2).

A plurality of cutters 40 is mounted on an exterior portion of each of said cutter bases 30. While various embodiments of cutters 40 may be used, one suitable embodiment uses a metal base or cutter plate which is attached to cutter base 30 by welding or similar means. In a preferred embodiment, said cutters 40 may be covered with carbide or other suitable hardened surface, or a combination of hardened material buttons and carbide or similar materials. However, it is to be observed that a variety of cutting surfaces are suitable, so long as they present a hardened surface to the surrounding casing to be engaged in order to permit milling of same.

In a preferred embodiment, cutters 40 are preferably arranged in a plurality of vertically spaced apart rows along a desired portion of the length of each cutter base 30. To facilitate milling in a downward direction, with conventional right-hand rotation of a drillstring, cutters 40 may be angled or inclined, wherein an upper end of cutters 40 may be inclined in a direction of rotation of wellbore cutting assembly 10. The number, position, and spacing of cutters 40 may be varied to suit particular applications.

With cutters 40 positioned in a plurality of vertically spaced apart, horizontally aligned rows, it can be appreciated that as milling progresses, and a row of cutters wears out, the diameter of the cutters decreases such that the next row of cutters above moves downward into contact with a surrounding casing surface to be cut or milled. In this manner, a fresh cutting surface is presented to a casing edge being milled. It can be appreciated that the multiple rows of cutters 40 permit cutting assembly 10 to remain in a wellbore for an extended period, thereby greatly reducing time spent in pulling and re-dressing cutting surfaces of said cutting assembly 10.

Although not visible in FIG. 5, body member 20 comprises an elongate central through bore. Lock ring sleeve 120 is disposed within said central through bore and anchored in place. A piston member 80 is also disposed in said central bore of body member 20. Piston member 80 has at least one lock button recess 90 formed in a side surface of said piston member 80. A lock button 110 is moveably disposed within each of said lock button recesses 90 as more fully described herein. A piston stop 84 and O-ring 91 are affixed to piston 80 using lock ring 92. Still referring to FIG. 5, it is to be observed that, for space and clarity, not all fittings and fasteners are labeled.

FIGS. 6A and 6B depict a side sectional view of a wellbore cutting assembly of the present invention along line 6-6 of FIG. 2 wherein cutter bases 30 are in a substantially collapsed or radially inward configuration. In the embodiment depicted in FIGS. 6A and 6B, said cutter bases 30 are generally disposed within recesses 28 of body member 20. FIGS. 7A and 7B depict a side sectional view of a wellbore cutting assembly 10 of the present invention along line 7-7 of FIG. 4 wherein cutter bases 30 are in a substantially extended or radially outward configuration. In the embodiment depicted in FIGS. 7A and 7B, said cutter bases 30 are not disposed within recesses 28 of body member 20, but are disposed in a radially outward position relative to body member 20.

Referring to FIGS. 6A/6B and 7A/7B, said wellbore cutting assembly 10 comprises ported sub 60 having a means for connection and operational attachment to a tubular workstring 200 which, in the embodiment depicted in FIGS. 6A/6B and 7A/7B, comprises female or “box-end” threaded connection member 62 Said ported sub 60 also has lower male or “pin-end” threaded connection 61 for attachment to body member 20. Central through bore 63 extends along the longitudinal axis of ported sub 60.

Body member 20 has elongate recesses 28 formed in the exterior of said body member 20. At least one cutter base 30 is operationally attached to body member 20. Upper linkage arms 50 are pivotally attached to body member 20 using upper pivot pins 52, and to said cutter bases 30 using pivot pins 53. Lower linkage arms 51 are pivotally attached to body member 20 using lower pivot pins 54, and to cutter base 30 using pivot pins 55. A plurality of cutters 40 is mounted on an exterior portion of each of said cutter bases 30.

Body member 20 has an elongate central through bore 26 extending at least partially along the length of said central body member 20. Lock ring sleeve 120 is disposed within said central through bore 26. Similarly, piston member 80 is moveably disposed within said bore 26, while piston stop 84 disposed within said central bore 26 of body member 20 to limit upward travel of said piston member 80. A lock button 110 is moveably disposed within each lock button recess 90 in said piston member 80.

Referring to FIGS. 7A/7B, cutter bases 30 are depicted in a radially outward or extended position. Generally, cutter bases 30 are sized so as to fit within the outer radius of body member 20 when retracted. The dimensions of positioning arms 50 and cutter bases 30 yield sufficient outward radius to position cutters 40 in a desired position relative to surrounding casing. Dimensions of cutter base 30 can therefore be dependent upon the size of casing being milled, and upon the dimensions of body member 20 and positioning arms 50. Likewise, the dimensions of cutters 40 in a radially outward direction may be adjusted as necessary to suit particular job parameters.

FIG. 8 depicts a detailed view of the highlighted portion of FIG. 6B. In a preferred embodiment, piston 80 has upper body section 81, lower extension section 83 and nose member 87. Lower extension section 83 is disposed between spaced-apart roller guide pins 25; said roller guide pins 25 are oriented substantially parallel to each other, and rotatably cooperate to keep lower extension section 83 centered within bore 26. A central through bore 82 extends along the length of upper body section 81, while central through bore 86 (typically having a smaller inner diameter than bore 82) extends along the length of lower extension section 83 and nose member 87. Nozzle member 85 defining flow port opening 85A is disposed in said central through bore 82. In a preferred embodiment, said nozzle member 85 is disposed at or near a junction between bores 82 and 86, while flow port opening 85A has a smaller diameter than through bore 82.

Piston 80 is moveably disposed in central through bore 26 of body member 20; as such, central through bore 82 of piston 80 has a smaller diameter than bore 26 of body member 20. Piston body section 82 further comprises at least one (typically three) transverse lock button recess 90, while a Lock button110 is moveably disposed within each said lock button recess 90. In the configuration depicted in FIG. 8, with cutter bases 30 collapsed radially inward, cutting assembly of the present invention can be conveyed or run in a wellbore (on a tubular drillstring or workstring) to a desired depth. During such operation, piston stop 84 prevents backward movement of piston 80 within bore 26 (that is, movement in the opposite axial direction away from cutter bases 30) while cutting assembly 10 is being conveyed in a wellbore.

FIG. 10 depicts a perspective exploded view of a locking assembly of the present invention. Lock button recesses 90 are formed in body section 81 of piston member 80 and are oriented in a substantially radially outward direction; in a preferred embodiment, piston member 80 has 3 lock button recesses 90 disposed in relationship around the circumference of piston 80. Transverse button mounting port 92, which is positioned in said lock button recess 90, extends through said body section 81 in a direction that is substantially perpendicular to the longitudinal axis of piston member 80.

Lock button110 has external ridges 111, outer channel 117 and rear extension 116. An elastomeric o-ring 112 is received on said rear extension 116; said rear extension 116 and o-ring 112 are slidably received within transverse mounting port 92. Lock button 110 is retained in place within recess 90 using spring 113 and spring retainer 114 secured to body section 80 using threaded fasteners 115 received in threaded bores 118. Spring 113 pushes against spring retainer 114, and acts to bias lock button 110 radially inward within lock button recess 90.

FIG. 9 depicts a detailed view of the highlighted portion of FIG. 7B. In operation, after cutter assembly 10 is conveyed in a wellbore and positioned at a desired depth within said wellbore, fluid can be selectively pumped down a drillstring or workstring and/or other components thereof, into bore 26 of body member 20. Because bore 82 of piston member 80 has a smaller diameter than bore 26 of body member 20, fluid pressure acts on said piston 80, thereby forcing piston 80 downward within through bore 26. More specifically, said fluid pressure forces nose member 87 to engage against cam-shaped heel extensions 56 of linkage arms 50, thereby causing each of said linkage arms 50 to rotate about pin 52. Rotatable roller guide pins 25 maintain lower extension 83 in a centered position within bore 26, while reducing frictional forces acting on said piston 80. As said linkage arms 50 each rotate about a pivot pin 52, cutter bases 30 (and cutters disposed thereon) are forced radially outward relative to body member 20.

FIG. 13 depicts a detailed side view of the highlighted portion of FIG. 8. Lock button110 has external ridges 111 and rear extension 116 with expanded end head 116A; elastomeric o-ring 112 is received on said rear extension 116. Rear extension 116 and o-ring 112 are slidably received within transverse mounting port 92 which is in fluid communication with—and oriented substantially perpendicular to—central through bore 82. As depicted in FIG. 10, lock button 110 is retained in place within recess 90 using spring 113 and spring retainer 114 secured to body section 80 using threaded fasteners 115. Referring back to FIG. 13, although not visible in said drawing, it is to be observed that spring 113 acts against spring retainer 114 to bias lock button 110 radially inward in the direction of through bore 82.

FIG. 14 depicts a detailed side view of the highlighted portion of FIG. 9. When said fluid is pumped through bore 82, expanded end head 116A of lock button 110 is exposed to said fluid pressure. Force from said fluid pressure acts on said end head 116A, causing said at least one lock button 110 to resist spring bias force (from spring 113) and move radially outward within transverse bore 92 until ridges 111 of lock button 110 engage against the inner surface of lock ring sleeve 120 (including internal ridges 121).

In a preferred embodiment, lock ring sleeve 120 has inwardly facing ridges 121 that are designed to hold loading in only one axial direction. Specifically, referring to FIG. 13, each of said ridges 121 comprises substantially horizontal surface 121A and tapered/sloped surface 121B. As such, lock button 110 and lock ring 120 cooperate to act as ratchet assembly; when lock button 110 is engaged, said ratchet assembly will provide resistance to prevent piston body 81 from moving axially upward, (and linkage arms 50 from collapsing), while allowing substantially free movement of piston 80 in an in opposite (downward) axial direction. When multiple lock buttons 110 are employed, loading acting on lock ring sleeve 120 is beneficially equally distributed between said lock button(s) 110.

FIG. 11 depicts a sectional view of a wellbore cutting assembly of the present invention along line 11-11 of FIG. 2 which is in a substantially retracted or collapsed configuration. Piston 80 has upper body section 81, while central through bore 82 extends along the length of upper body section 81. Nozzle member 85 defining flow port opening 85A is disposed in said central through bore 82. Lock buttons110 each have a rear extension 116 slidably received within a transverse mounting port 92 which is in fluid communication with—and oriented substantially perpendicular to—central through bore 82. Each lock button 110 is retained in place within a recess 90 using spring 113 and spring retainer 114; spring 113 acts against spring retainer 114 to bias lock button 110 radially inward in the direction of through bore 82.

During operation within a wellbore, the present invention will ensure that cutter bases 30 do not collapse radially inward toward main body 20, particularly when said cutting assembly 10 is used in relatively small casings or casings with flush connections. Further, when the pumping of fluid ceases, a differential pressure acting on lock button(s) 110 will also cease, thereby allowing spring(s) 113 to bias said lock button(s) 110 away from lock ring sleeve 120. In this manner, linkage arms 50 and 51 can be easily collapsed inward (resulting in cam shaped heel extensions 56 “pushing” piston member within bore 26), such as when fluid pumping ceases and/or cutting assembly 10 is being retrieved or pulled out of a wellbore.

FIG. 12 depicts a sectional view of a wellbore cutting assembly of the present invention along line 12-12 of FIG. 2. In the event that said lock button(s) do not recede or piston 80 does not move as desired when pumping of fluid ceases, cutting assembly 10 can be picked up within a wellbore using a tubular drillstring. In such a scenario, the axial force applied to said cooperating lock button(s) 110 and lock sleeve 120 can be increased until shear screw(s) 130, which are received in bores 29 and hold lock ring sleeve 120 in place within body member 20, shear at a predetermined or preset force. When this occurs, lock ring sleeve 120 is permitted to move axially within bore 26 of body member 20, thereby disengaging from said lock button(s) 110 and permitting said linkage arms 50 to collapse radially inward toward said body member 20.

By way of illustration, but not limitation, and without confining the current invention to any particular configuration or operating mechanism, it is to be observed that U.S. Patent Applicant Publication No. 2017/0298705 discloses an embodiment of cutting assembly that can be utilized with the locking assembly of the present invention. The disclosure of said patent application is incorporated herein by reference to the extent necessary to illustrate an exemplary tool configuration and/or operating mechanism thereof. Nonetheless, it is also to be observed that the locking mechanism of the present invention can also be beneficially employed with other cutting tools or devices.

In a preferred embodiment, said central through bore 26 extends sufficiently far along the length of body member 20 to route fluid to the positioning arm area, but bore 26 typically should not run the entire length of body member 20. By having only a partial length bore, and forcing fluid to exit the tool through transverse flow ports in the vicinity of positioning arms 50 and the recess(es) 28 in body member 20 into which cutter bases 30 retract, fluid flow tends to keep these surfaces flushed and relatively free of cuttings and debris.

While the preceding description contains many specificities, it is to be understood that same are presented only to describe some of the presently preferred embodiments of the invention, and not by way of limitation. Changes can be made to various aspects of the invention, without departing from the scope thereof. For example, dimensions of the various components of the tool can be varied to suit particular jobs; the number of cutter bases can be varied; the number and positioning of cutters per cutter base can be varied; size and shape of the cutters can vary; the angle of the cutters on the cutter bases (that is, the angle with respect to the longitudinal axis of the tool) can be adjusted; the number, size, and placement of the tungsten carbide (or other suitable material) buttons on the cutters can be varied; the configuration of the face surfaces (both as to their multi-sided shape, and the depressions in the face) of tungsten carbide buttons can be varied to provide the most efficient “chip breaker” shape for the application; and methods of use can be varied.

The above-described invention has a number of particular features that should preferably be employed in combination, although each is useful separately without departure from the scope of the invention. While the preferred embodiment of the present invention is shown and described herein, it will be understood that the invention may be embodied otherwise than herein specifically illustrated or described, and that certain changes in form and arrangement of parts and the specific manner of practicing the invention may be made within the underlying idea or principles of the invention. 

1. An apparatus for downhole cutting or milling in a wellbore comprising: a) a body member having a central through bore; b) at least one cutter base hingedly attached to said body member, wherein said at least one cutter base is configured to alternate between a first radially collapsed position and a second radially extended position; c) a piston, having a central through bore, moveably disposed within said through bore of said body member, wherein said piston is configured to alternate between a first position, and a second position wherein said piston forces said at least one cutter base to shift from said first collapsed position to said second extended position; and d) at least one cutter disposed on said at least one cutter base.
 2. The apparatus of claim 1, further comprising a locking assembly configured to lock said at least one cutter base in said second radially extended position.
 3. The apparatus of claim 2, wherein said locking assembly further comprises: a) a locking sleeve disposed in said central bore through bore of said body member between said body member and said piston; b) at least one lock button operationally attached to said piston, wherein said at least lock button is configured to alternate between a first retracted position and a second extended position in engagement with said locking sleeve.
 4. The apparatus of claim 3, wherein said locking sleeve further comprises ridges disposed on an inner surface of said locking sleeve, and said at least one lock button further comprises ridges disposed on an outer surface of said at least one lock button.
 5. The apparatus of claim 4, wherein said at least one lock button is received within a recess in said piston.
 6. The apparatus of claim 5, wherein said locking sleeve is secured to said body member with at least one shear pin
 7. The apparatus of claim 6, wherein said at least one shear pin is configured to separate in response to a predetermined force, causing said locking sleeve to detach from said body member.
 8. The apparatus of claim 1, further comprising a nozzle having a predetermined opening disposed in said central through bore of said piston
 9. An apparatus for downhole cutting or milling in a wellbore comprising: a) a body member having a central through bore; b) at least one cutter base hingedly attached to said body member, wherein each of said at least one cutter base has a heel member protruding into said central bore of said body member; c) a piston, having a central through bore, moveably disposed within said through bore of said body member, wherein said piston is configured to alternate between a first position, and a second position wherein said piston acts on said heel member and forces said at least one cutter base to shift from a first collapsed position to second radially extended position; and d) at least one cutter disposed on said at least one cutter base.
 10. The apparatus of claim 9, further comprising a locking assembly configured to lock said at least one cutter base in said second radially extended position.
 11. The apparatus of claim 10, wherein said locking assembly further comprises a) a locking sleeve disposed in said central bore through bore of said body member between said body member and said piston; b) at least one lock button operationally attached to said piston, wherein said at least lock button is configured to alternate between a first retracted position and a second extended position in engagement with said locking sleeve.
 12. The apparatus of claim 11, wherein said locking sleeve further comprises ridges disposed on an inner surface of said locking sleeve, and said at least one lock button further comprises ridges disposed on an outer surface of said at least one lock button.
 13. The apparatus of claim 12, wherein said at least one lock button is received within a recess in said piston.
 14. The apparatus of claim 13, wherein said locking sleeve is secured to said body member with at least one shear pin.
 15. The apparatus of claim 14, wherein said at least one shear pin is configured to separate in response to a predetermined force, causing said locking sleeve to detach from said body member.
 16. The apparatus of claim 9, further comprising a nozzle having a predetermined opening disposed in said central through bore of said piston. 